As surely as the buds expand in the spring

 From "Spring" in Walden, originally written on February 12, 1854.

The pond began to boom about an hour after sunrise, when it felt the influence of the sun's rays slanted upon it from over the hills; it stretched itself and yawned like a waking man with a gradually increasing tumult, which was kept up three or four hours. . . . The pond does not thunder every evening, and I cannot tell surely when to expects is thundering; but though I may perceive no difference in the weather, it does.  Who would have suspected so large and cold and thick-skinned a thing to be so sensitive? Yet it has its laws to which it thunders obedience when it should as surely as the buds expand in the spring.  The earth is all alive and covered with papillae.  The largest pond is as sensitive to atmosphere changes as the globule of mercury in its tube.

A polar vortex has taken hold in the midwest, and there's not been a more than a 2-day break between snow showers or snow storms for weeks, it seems.  It was -8 last week and -6 yesterday.  But underneath the snow and cold, the earth is surely changing.  Trees are gathering energy to flower and leaf.  Crocuses are just waiting to burst forth. 

The metaphor comparing the pond to a thermometer is so good.  On the one hand, it's literally true that all things are little tubes of mercury -- it's a matter of physics of temperature.  Just now, I heard the house creak with the cold.  On the other hand, it points to an image of interconnectedness and an expansive world view, an animate earth responding to the sun.  It erases the difference between human and natural environment; it suggests that we all respond to the grand influences of season and sun. . . . and that natural cycle is predictable and expected.